CD4+ T helper cells are not a homogeneous population but can be divided on the basis of cytokine secretion into at least two subsets termed T helper type 1 (Th1) and T helper type 2 (Th2) (see e.g., Mosmann, T. R. et al. (1986) J. Immunol. 136:2348-2357; Paul, W. E. and Seder, R. A. (1994) Cell 76:241-251; Seder, R. A. and Paul, W. E. (1994) Ann. Rev. Immunol. 12:635-673). Thl cells secrete interleukin-2 (IL-2) and interferon-.gamma. (IFN-.gamma.) while Th2 cells produce interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-10 (IL-10) and interleukin-13 (IL-13). Both subsets produce cytokines such as tumor necrosis factor (TNF) and granulocyte/macrophage-colony stimulating factor (GM-CSF). In addition to their different pattern of cytokine expression, Th1 and Th2 cells are thought to have differing functional activities. For example, Th1 cells are involved in inducing delayed type hypersensitivity responses, whereas Th2 cells are involved in providing efficient "help" to B lymphocytes and stimulating production of IgG1 and IgE antibodies.
There is now abundant evidence that the ratio of Th1 to Th2 cells is highly relevant to the outcome of a wide array of immunologically-mediated clinical diseases including autoimmune, allergic and infectious diseases. For example, in experimental leishmania infections in mice, animals that are resistant to infection mount predominantly a Th1 response, whereas animals that are susceptible to progressive infection mount predominantly a Th2 response (Heinzel, F. P., et al. (1989) J. Exp. Med. 169:59-72; Locksley, R. M. and Scott, P. (1992) Immunoparasitology Today 1:A58-A61). In murine schistosomiasis, a Th1 to Th2 switch is observed coincident with the release of eggs into the tissues by female parasites and is associated with a worsening of the disease condition (Pearce, E. J., et al. (1991) J. Exp. Med. 173:159-166; Grzych, J -M., et al. (1991) J. Immunol. 141:1322-1327; Kullberg, M. C., et al. (1992) J. Immunol. 148:3264-3270). Many human diseases, including chronic infections (such as with human immunodeficiency virus (HIV) and tuberculosis) and certain metastatic carcinomas, also are characterized by a Th1 to Th2 switch (see e.g., Shearer, G. M. and Clerici, M. (1992) Prog. Chem. Immunol. 54:21-43; Clerici, M and Shearer, G. M. (1993) Immunology Today 14:107-1 11; Yamamura, M., et al. (1993) J. Clin. Invest. 91:1005-1010; Pisa, P., et al. (1992) Proc. Natl. Acad. Sci. USA 89:7708-7712; Fauci, A. S. (1988) Science 239:617-623). Furthermore, certain autoimmune diseases have been shown to be associated with a predominant Th1 response. For example, patients with rheumatoid arthritis have predominantly Th1 cells in synovial tissue (Simon, A. K., et al. (1994) Proc. Natl. Acad. Sci. USA 91:8562-8566) and experimental autoimmune encephalomyelitis (EAE) can be induced by autoreactive Th1 cells (Kuchroo, V. K., et al. (1993) J. Immunol. 151:4371-4381).
The ability to alter or manipulate ratios of Th1 and Th2 subsets requires an understanding of the mechanisms by which the differentiation of CD4 T helper precursor cells (Thp), which secrete only IL-2, choose to become Th1 or Th2 effector cells. It is clear that the cytokines themselves are potent Th cell inducers and form an autoregulatory loop (see e.g., Paul, W. E. and Seder, R. A. (1994) Cell 76:241-251; Seder, R. A. and Paul, W. E. (1994) Ann. Rev. Immunol. 12:635-673). Thus, IL-4 promotes the differentiation of Th2 cells while preventing the differentiation of precursors into Th1 cells, while IL-12 and IFN-.gamma. have the opposite effect. One possible means therefore to alter Th1:Th2 ratios is to increase or decrease the level of selected cytokines. Direct administration of cytokines or antibodies to cytokines has been shown to have an effect on certain diseases mediated by either Th1 or Th2 cells. For example, administration of recombinant IL-4 or antibodies to IL-12 ameliorate EAE, a Th1-driven autoimmune disease (see Racke; M. K. et al. (1994) J. Exp. Med. 180:1961-1966; and Leonard, J. P. etal. (1995) J. Exp. Med. 181:381-386), while anti-IL-4 antibodies cure the Th2-mediated parasitic disease, Leishmania major (Sadick, M. D. et al. (1990) J. Exp. Med. 171:115-127). However, as therapeutic options, systemic administration of cytokines or antibodies may have unwanted side effects and, accordingly, alternative approaches to manipulating Th1/Th2 subsets are still needed.
While the molecular basis for the tissue-specific expression of T cell cytokines has remained elusive, study of the transcriptional elements of cytokine genes has provided insight into their regulation. Analysis of the IL-4 cytokine promoter, for example, has revealed functionally critical sites for several transcription factors including members of the NF-AT and AP-1 families (Rooney, J. W. et al. (1995) Immunity 2:473-483; Szabo, S. J. et al. (1993) Mol. Cell. Biol. 13:4793-4805). NF-AT is a multisubunit transcription complex that contains a cyclosporin A sensitive cytoplasmic phosphoprotein and an inducible nuclear component composed of AP-1 family member proteins (Flanagan, W. M. et al. (1991) Nature 352:803-807; Jain, J. et al. (1992) Nature 356:801-804). Purification and cloning of NF-ATp revealed a region of limited sequence identity to the Rel Homology Domain (RHD) of the NF.kappa.B family of transcription factors (McCaffrey, P. G. et al. (1993) Science 262:750-754). Subsequent cloning and sequencing of three related genes, NF-ATc, NF-AT4/x/c3, and NF-AT3/c4 revealed similar domains. NF-AT family members share approximately 70% sequence similarity within this domain and approximately 18% sequence similarity to the RHD of the Rel/NF.kappa.B family of transcription factors. Consistent with their very limited sequence similarity in the RHD, there are marked differences in the behavior of NF.kappa.B and NF-AT proteins, and much less is known about the pathways that mediate transcriptional regulation of NF-AT target genes. However, considering that NF-AT family members can bind to and transactivate the promoters of multiple cytokine genes including IL-2 and IL-4 (Rooney, J. et al. (1995) Immunity 2:545-553; Szabo, S. J. et al. (1993) Mol. Cell. Biol. 13:4793-4805; Flanagan, W. M. et al. (1991) Nature 352:803-807; Northrop, J. P. et al. (1994) Nature 369:497), NF-AT proteins are not likely to be directly responsible for mediating Th1- or Th2-specific cytokine transcription.
Most, if not all, NF-AT binding sites in cytokine promoter regulatory regions are accompanied by nearby sites that bind auxiliary transcription factors, usually members of the AP-1 family. It has been shown that NF-AT and AP-1 proteins bind coordinately and cooperatively and are required for full activity of the IL-2 and IL-4 promoters. Different AP-1 proteins, specifically c-Jun, c-Fos, Fra-1, Fra-2, Jun B and Jun D, have been shown to bind to these sites (Rao, A. et al (1994) Immunol. Today 15:274-281; Jain, J. et al. (1993) Nature 365:352-355; Boise, L. H. et al. (1993) Mol. Cell. Biol. 13:1911-1919; Rooney, J. et al. (1995) Immunity 2:545-553; Rooney, J. et al. (1995) Mol. Cell. Biol. 15:6299-6310). However, none of these AP-1 proteins is expressed in a Th1- or Th2-specific manner and there is no evidence for the differential recruitment of AP-1 family members to the IL-2 or IL-4 composite sites (Rooney, J. et al. (1995) Mol. Cell. Biol. 15:6299-6310). Thus, neither NF-AT proteins nor the AP-1 family members c-Jun, c-Fos, Fra-1, Fra-2, Jun B and Jun D can account for the tissue-specific transcription of IL-4 in Th2 cells.
In the related co-pending application U.S. Ser. No. 08/636,602, U.S. Pat. No. 5,958,671, we have provided evidence that the selective expression of the proto-oncogene c-maf in Th2 cells is responsible for tissue-specific IL-4 expression. Interestingly, c-Maf acts in synergy with NF-AT proteins to transactivate the IL-4 promoter. This is consistent with previous data that the inducible expression of multiple cytokine genes and cell surface proteins following T cell receptor stimulation requires members of the NF-AT transcription factor family (Rooney, J. W. et al. (1995) Immunity 2:473-483; Cockerill, P. N. et al. (1995) Mol. Cell. Biol. 15:2071-2079; Goldfeld, A. E. et al. (1993) J. Exp. Med. 178:1365-1379; Shaw, J. P. et al. (1988) Science 241:202-205). However, it was unknown, prior to the present invention, whether additional proteins exist that act in concert with known transcriptional activators, such as NF-AT and c-Maf, to activate cytokine gene expression.